// Copyright 2009 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_REGEXP_REGEXP_STACK_H_
#define V8_REGEXP_REGEXP_STACK_H_

#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/globals.h"

namespace v8 {
namespace internal {

    class RegExpStack;

    // Maintains a per-v8thread stack area that can be used by irregexp
    // implementation for its backtracking stack.
    // Since there is only one stack area, the Irregexp implementation is not
    // re-entrant. I.e., no regular expressions may be executed in the same thread
    // during a preempted Irregexp execution.
    class RegExpStackScope {
    public:
        // Create and delete an instance to control the life-time of a growing stack.

        // Initializes the stack memory area if necessary.
        explicit RegExpStackScope(Isolate* isolate);
        ~RegExpStackScope(); // Releases the stack if it has grown.

        RegExpStack* stack() const { return regexp_stack_; }

    private:
        RegExpStack* regexp_stack_;

        DISALLOW_COPY_AND_ASSIGN(RegExpStackScope);
    };

    class RegExpStack {
    public:
        // Number of allocated locations on the stack below the limit.
        // No sequence of pushes must be longer that this without doing a stack-limit
        // check.
        static const int kStackLimitSlack = 32;

        // Gives the top of the memory used as stack.
        Address stack_base()
        {
            DCHECK_NE(0, thread_local_.memory_size_);
            return reinterpret_cast<Address>(thread_local_.memory_) + thread_local_.memory_size_;
        }

        // The total size of the memory allocated for the stack.
        size_t stack_capacity() { return thread_local_.memory_size_; }

        // If the stack pointer gets below the limit, we should react and
        // either grow the stack or report an out-of-stack exception.
        // There is only a limited number of locations below the stack limit,
        // so users of the stack should check the stack limit during any
        // sequence of pushes longer that this.
        Address* limit_address() { return &(thread_local_.limit_); }

        // Ensures that there is a memory area with at least the specified size.
        // If passing zero, the default/minimum size buffer is allocated.
        Address EnsureCapacity(size_t size);

        // Thread local archiving.
        static int ArchiveSpacePerThread()
        {
            return static_cast<int>(sizeof(ThreadLocal));
        }
        char* ArchiveStack(char* to);
        char* RestoreStack(char* from);
        void FreeThreadResources() { thread_local_.Free(); }

    private:
        RegExpStack();
        ~RegExpStack();

        // Artificial limit used when no memory has been allocated.
        static const Address kMemoryTop = static_cast<Address>(static_cast<uintptr_t>(-1));

        // Minimal size of allocated stack area.
        static const size_t kMinimumStackSize = 1 * KB;

        // Maximal size of allocated stack area.
        static const size_t kMaximumStackSize = 64 * MB;

        // Structure holding the allocated memory, size and limit.
        struct ThreadLocal {
            ThreadLocal() { Clear(); }
            // If memory_size_ > 0 then memory_ must be non-nullptr.
            byte* memory_;
            size_t memory_size_;
            Address limit_;
            void Clear()
            {
                memory_ = nullptr;
                memory_size_ = 0;
                limit_ = kMemoryTop;
            }
            void Free();
        };

        // Address of allocated memory.
        Address memory_address()
        {
            return reinterpret_cast<Address>(&thread_local_.memory_);
        }

        // Address of size of allocated memory.
        Address memory_size_address()
        {
            return reinterpret_cast<Address>(&thread_local_.memory_size_);
        }

        // Resets the buffer if it has grown beyond the default/minimum size.
        // After this, the buffer is either the default size, or it is empty, so
        // you have to call EnsureCapacity before using it again.
        void Reset();

        ThreadLocal thread_local_;
        Isolate* isolate_;

        friend class ExternalReference;
        friend class Isolate;
        friend class RegExpStackScope;

        DISALLOW_COPY_AND_ASSIGN(RegExpStack);
    };

} // namespace internal
} // namespace v8

#endif // V8_REGEXP_REGEXP_STACK_H_
